Transmission and power grid wire is aluminum - it is 4-8 times cheaper than copper. And aluminum

Connection

Connection is more difficult than copper
One only wire nut exists that is UL approved - source - [1] since 1995 - wikipedia [2]. Not cheap.
Aluminum can be soldered, or welded.
Inspectors - Al wiring is allowed for the home - [3]. Push-in quick connect for aluminum is not allowed. In general, aluminum wiring is doable, but not recommended due to the extra challenges. Crimp end from al to cu can be done for retrofit of aluminum wire to standard wire.

Aluminum Wire